Either nothing or a 2-part epoxy finish.
I've used the 2-part epoxy for wine goblets and such. Primarily to prevent staining. Imagine what the inside of a maple bowl would look like after a tomato based soup....
But usually the soup gets eaten too quickly to worry about anything. So natural is a good thing. A renewable finish like carnuba wax is okay - if you have care and feeding instructions included with your bowl.